The present invention relates to an apparatus for ultrasonic color flow mapping for diagnosis use, and in particular to an apparatus and a method capable of removing artifact due to movement of body organs to obtain correct display of blood flow.
An ultrasonic flood flow mapping apparatus displays the velocity and the direction of blood flow in a heart or an abdominal region two-dimensionally, using the Doppler effect. Since it is possible to recognize visually distribution of blood vessel in a living body by superposing an image thus obtained on a section image to display them together, it is often utilized at present in clinical sites. For example, JP-A-60-96232 (1985) discloses this technique.
In this apparatus, reflected waves from sampling points on a B-mode section are detected one after another by transmitting and receiving repeatedly ultrasonic pulses accompanying beam scanning to obtain phase signals indicating the phase of detected signals by complex data processing one after another. The phase shift of a signal from a sampling point corresponding to a specified transmission interval is calculated to obtain the velocity of a moving target at that point. Variations in this velocity are represented by numerical values or a graph, which are displayed at respective positions corresponding to the B-mode section, superposed on a B-mode image. In order to avoid influences of signals from body organs such as vessel wall, etc. on values representing this displacement velocity, digital filters having high pass characteristics called delay line cancelers or MTI filters (moving target indicating filters) are used. The velocity thus displayed is supposed to represent the blood flow velocity in a blood vessel.
Apart therefrom various blood flow mapping apparatuses have been proposed. For example, devices have been made, by which the B-mode step loading is displayed in a gray scale and the blood flow velocity superposed thereon is displayed in different color tones, etc.
In the field of diagnosis of the abdominal region such as the liver, the kidney, etc., blood flow information of extremely low velocity, which is as low as about 3 cm/sec is useful. It is difficult to separate signals for blood flow of this degree of velocity from signals due to movement of body organs themselves produced by movement of body, respiration, etc. by means of MTI filters having high pass characteristics as used heretofore. That is, if the band of the signal cut in the neighborhood of a point, where the phase shift is zero, is extended, blood flow information of low velocity is removed also by the MTI filters. On the contrary, if the band of the signal cut is narrowered, signal components due to movement of the body organs are mixed in the flow velocity signal and therefore artifact is mixed in the blood velocity display.